The present invention relates to a ceramic and aluminum alloy composite having an improved bonding strength between the members of the composite.
Aluminum alloys are lightweight, strong, easily machinable and have excellent electrical and heat conducting properties. Because of these advantages, aluminum alloys are extensively used in low-temperature applications. However, their service at high temperatures is limited, largely due to their poor heat resistance and heat insulating ability.
Ceramics on the other hand have excellent heat resisting and insulating properties. Numerous attempts have been made to eliminate the defects of aluminum alloys by combining them with ceramics into ceramic-aluminum alloy composites. However, none of the methods that have been proposed to date for bonding ceramics to aluminum alloys achieve completely satisfactory results. The most favorable approaches are the techniques of shrink fitting and casting, but even these provide only composites of low thermal reliability due not only to the inherent thermal expansion coefficient mismatch between aluminum and ceramics but also to aluminum failure. Aluminum has a thermal expansion coefficient of 24.times.10.sup.-6 /.degree.C. at temperatures between room temperature and 500.degree. C., whereas Si.sub.3 N.sub.4 and ZrO.sub.2, which are two typical ceramics, have respective thermal expansion coefficients of 2.times.10.sup.-6 /.degree.C. and 10.times.10.sup.-6 /.degree.C. in the same temperature range. Because of this thermal expansion coefficient mismatch, a ceramic cannot be directly bonded to aluminum without producing a residual stress that often leads to cracking of the ceramic.